/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlinePartyInterface.h
Reject an invite to a party
true if task was started
bool RejectInvitation ( const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & LocalUserId, const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & SenderId )